U.S. patent application number 11/783749 was filed with the patent office on 2007-10-25 for cellular network resource control method and apparatus.
This patent application is currently assigned to TELEFONAKTIEBOLAGET LM ERICSSON (PUBL). Invention is credited to Bo Ove Hagerman, Kimmo Juhani Hiltunen.
Application Number | 20070249340 11/783749 |
Document ID | / |
Family ID | 33484845 |
Filed Date | 2007-10-25 |
United States Patent
Application |
20070249340 |
Kind Code |
A1 |
Hiltunen; Kimmo Juhani ; et
al. |
October 25, 2007 |
Cellular network resource control method and apparatus
Abstract
A cellular radio access network comprising a plurality of radio
transceivers geographically spaced so that neighbouring
transceivers provide overlapping radio coverage for mobile user
terminals, and a radio transceiver controller geographically spaced
from and coupled to said plurality of radio transceivers, the
controller being arranged to control each radio transceiver so that
neighbouring transceivers can be configured to communicate with
user terminals using either the same or different radio channels,
whereby the effective cell sizes of the radio access network can be
dynamically increased or decreased depending upon the demands
placed on the available radio resources.
Inventors: |
Hiltunen; Kimmo Juhani;
(Stockholm, SE) ; Hagerman; Bo Ove; (Tyreso,
SE) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
TELEFONAKTIEBOLAGET LM ERICSSON
(PUBL)
Stockholm
SE
|
Family ID: |
33484845 |
Appl. No.: |
11/783749 |
Filed: |
April 11, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/EP05/55166 |
Oct 11, 2005 |
|
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|
11783749 |
Apr 11, 2007 |
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Current U.S.
Class: |
455/433 |
Current CPC
Class: |
H04W 16/06 20130101 |
Class at
Publication: |
455/433 |
International
Class: |
H04Q 7/20 20060101
H04Q007/20 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 20, 2004 |
GB |
0423248.4 |
Claims
1. A method of providing mobile user terminals with access to a
cellular radio access network, the method comprising: defining
logical cells each comprising a set of sub-areas, each sub-area
containing a radio transceiver for communicating with user
terminals, and the sub-areas of a logical cell sharing one or more
sets of downlink common control channels; and for each logical
cell, dynamically allocating one or more sub-areas to each user
terminal within that logical cell, the sub-areas allocated to each
user terminal transmitting and/or receiving the same dedicated
information to/from the user terminal.
2. A method according to claim 1, wherein sub-areas are allocated
to user terminals on the basis of received uplink signal strengths
for terminals for sub-areas.
3. A method according to claim 1, wherein sub-areas are allocated
to user terminals on the basis of the measured or estimated uplink
quality.
4. A method according to claim 1, wherein sub-areas are allocated
to user terminals on the basis of the measured or estimated uplink
quality and said uplink quality is the Carrier-to-Interference
Ratio per sub-area per user terminal.
5. A method according to claim 1, wherein said logical cells are
dynamically configurable in terms of the sub-areas that they
contain.
6. A method according to claim 1, wherein said radio access network
is a CDMA network.
7. A method according to claim 6, and comprising identifying
hot-spots within a given logical cell, and allocating the primary
scrambling code to user terminals within the hotspots and secondary
scrambling codes to terminals outside the hotspots.
8. A method according to claim 1, and comprising allocating
sub-areas to a user terminal in dependence upon the speed of travel
of the user terminal and/or radio propagation conditions.
9. A method according to claim 1, the step of dynamically
allocating one or more sub-areas to each user terminal comprising
allocating sub-areas to user terminals in dependence upon the
service required by a user terminal.
10. A method according to claim 1, and comprising defining for a
user terminal an active set of logical cells to which the user is
connected, and said step of dynamically allocating one or more
sub-areas to each user terminal comprising allocating sub-areas
from the combined group of logical cells within the active set.
11. A method according to claim 1, said step of dynamically
allocating one or more sub-areas to each user terminal comprising
allocating different sets of sub-areas for the uplink and downlink
directions.
12. A method according to claim 1, wherein said dedicated
information is sent on one or more dedicated channels.
13. A radio transceiver controller comprising means for defining
logical cells comprising a set of sub-areas, each sub-area
containing a radio transceiver for communicating with user
terminals, and the sub-areas of a logical cell sharing one or more
sets of downlink common control channels and, for each logical
cell, the means being further arranged to dynamically allocate one
or more sub-areas to each user terminal within that logical cell,
the sub-areas allocated to each user transmitting and/or receiving
the same dedicated information to/from the user.
14. A method of providing mobile user terminals with access to a
cellular radio access network, the method comprising: defining
logical cells each comprising a set of sub-areas, each sub-area
containing a radio transceiver for communicating with user
terminals, and the sub-areas of a logical cell sharing one or more
sets of downlink common control channels; and for each logical
cell, dynamically allocating one or more sub-areas to each user
terminal within that logical cell, the sub-areas allocated to each
user terminal transmitting and/or receiving the different dedicated
information to/from the user terminal.
15. A method according to claim 14, each sub-area allocated to a
user terminal transmitting dedicated information to the user
terminal over a different dedicated downlink channel.
16. A radio transceiver controller comprising means for defining
logical cells comprising a set of sub-areas, each sub-area
containing a radio transceiver for communicating with user
terminals, and the sub-areas of a logical cell sharing one or more
sets of downlink common control channels and, for each logical
cell, the means being further arranged to dynamically allocate one
or more sub-areas to each user terminal within that logical cell,
the sub-areas allocated to each user transmitting and/or receiving
the different dedicated information to/from the user.
17. A radio transceiver controller according to claim 16, said
means being arranged to cause the allocated sub-areas to transmit
different dedicated information to the user terminals over
respective dedicated downlink channels.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a cellular network resource
control method and apparatus.
BACKGROUND TO THE INVENTION
[0002] Typically, in a cellular radio telecommunications system
such as GSM or UMTS, the whole system coverage area is divided into
smaller sub-areas, termed "logical cells". In general, the logical
cells are defined by the transmission of the downlink common
channels: in the neighbouring logical cells the downlink common
channels are typically transmitted on different frequencies and/or
using different scrambling codes or with other types of
identifiers.
[0003] Within each logical cell the amount of radio resources is
usually limited. That is why, in order to serve a higher user
density, the size of the logical cells has to be made smaller.
Furthermore, since the system resources are also limited, for
example the number of frequencies and the number of scrambling
codes, the same frequencies or scrambling codes must be re-used
(although only for cells which are spaced apart sufficiently to
avoid cross-cell interference).
[0004] U.S. Pat. No. 5,889,494 teaches a system and method for
dynamically sizing sectors of a multi-sectored radiation pattern
used in a cellular telecommunication system.
SUMMARY OF THE INVENTION
[0005] The great problem in the traditional cellular radio network
implementation is the lack of adaptivity. In a network where the
levels of user-related traffic can have relatively large dynamic
variations, those high loaded parts of the network can easily
become congested, while in low loaded areas the usage of the radio
resources can be relatively inefficient. In the case of a static
traffic distribution, a solution to geographically varying traffic
levels would be to decrease the cell size at the high loaded areas.
But with a traffic distribution which varies both geographically
and with time, i.e. where the traffic "hot spots" are not constant,
this kind of solution would not be particularly effective.
[0006] It is an object of the present invention to overcome or at
least mitigate the above noted disadvantages of prior art cellular
radio communication networks. This and other objects are achieved
by providing a mechanism for dynamically increasing or decreasing
cell size depending upon levels of demand.
[0007] According to a first aspect of the present invention there
is provided a cellular radio access network comprising:
[0008] a plurality of radio transceivers geographically spaced so
that neighbouring transceivers provide overlapping radio coverage
for mobile user terminals; and
[0009] a radio transceiver controller geographically spaced from
and coupled to said plurality of radio transceivers, the controller
being arranged to control each radio transceiver so that
neighbouring transceivers can be configured to communicate with
user terminals using either the same or different radio
channels,
[0010] whereby the effective cell sizes of the radio access network
can be dynamically increased or decreased depending upon the
demands placed on the available radio resources.
[0011] Cell sizes may be increased or decreased by combining and/or
splitting existing cells.
[0012] In one embodiment of the present invention, said access
network is a UMTS Radio Access Network, said radio transceiver
controller being provided by a Radio Network Controller and said
radio transceivers being provides by Node Bs.
[0013] The radio transceiver controller may comprise signal
processing means for processing radio signals received at the
transceivers and sent to the controller, and for processing signals
to be sent to the transceivers. The signal processing means is
arranged to combine signals received from different transceivers
and originating from a single user terminal.
[0014] The minimum functionality provided in a radio transceiver is
a downlink power amplifier, a low noise amplifier for the uplink,
and possibly some functionality for uplink measurements. The uplink
and downlink signal processing requirements are implemented at the
radio transceiver controller.
[0015] Said radio transceiver controller is arranged to manage
individual calls ongoing at the time of a cell size change. This
may involve handing over calls to a new channel, e.g. code or
frequency or time, or maintaining ongoing calls on existing
channels whilst setting up subsequent calls on new channels.
[0016] According to a second aspect of the present invention there
is provided a method of providing mobile user terminals with access
to a cellular radio access network, the method comprising:
[0017] monitoring levels of demand for radio resources within
individual cells of the radio access network; and;
[0018] increasing or decreasing the sizes of cells, including
combining and/or splitting cells in response to the monitored
demand levels.
[0019] According to a third aspect of the present invention there
is provided a method of providing mobile user terminals with access
to a cellular radio access network, the method comprising:
[0020] defining logical cells each comprising a set of sub-areas,
each sub-area containing a radio transceiver for communicating with
user terminals, and the sub-areas of a logical cell sharing one or
more sets of downlink control channels; and
[0021] for each logical cell, dynamically allocating one or more
sub-areas to each user terminal within that logical cell, the
sub-areas allocated to each user transmitting and/or receiving the
same information to/from the user.
[0022] According to a fourth aspect of the present invention there
is provided a radio transceiver controller comprising means for
defining logical cells comprising a set of sub-areas, each sub-area
containing a radio transceiver for communicating with user
terminals, and the sub-areas of a logical cell sharing one or more
sets of downlink control channels and, for each logical cell,
dynamically allocating one or more sub-areas to each user terminal
within that logical cell, the sub-areas allocated to each user
transmitting and/or receiving the same information to/from the
user.
[0023] According to a fifth aspect of the present invention there
is provided a method of providing mobile user terminals with access
to a cellular radio access network, the method comprising:
[0024] for each of a plurality of carrier frequencies, defining
logical cells each comprising a set of sub-areas, each sub-area
containing a radio transceiver for communicating with user
terminals, and the sub-areas of a logical cell sharing one or more
sets of downlink control channels, whereby the geographical
coverage of logical cells of different carrier frequencies
overlap.
BRIEF DESCRIPTION OF THE FIGURES
[0025] FIGS. 1 to 3 illustrate a system area of a radio access
network sub-divided into sub-areas and configured into logical
cells of respective different sizes;
[0026] FIG. 4 illustrates a system area controlled by a system
controller;
[0027] FIG. 5 illustrates a system area for the purpose of
illustrating a soft-handover scenario; and
[0028] FIG. 6 illustrates a system area for the purpose of
illustrating mechanism for locally increasing network capacity.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
[0029] As a solution to the problem of how to handle time-varying
traffic levels in a radio access network, the size of the logical
cells can be made dynamically flexible, so that they depend for
example on the capacity required. The key assumption behind this
solution is that the whole system area under consideration, as
illustrated by the solid line in FIG. 1, is divided into a number
of sub-areas "A" separated in the Figure by dashed lines, each one
covered for example by a separate antenna lobe, passive antenna (or
antenna system), or an active radio access port, see FIG. 1. As a
simple example, the system area can be assumed to be a building
within which cellular system coverage is desired.
[0030] In a low loaded network, the size of the logical cells can
be large. Thus, several sub-areas can be combined into one logical
cell, for example by transmitting the same downlink control
channels using the same scrambling code for all sub-areas. In such
a case, a mobile user terminal perceives this combination of
sub-areas as one logical cell. In the scenario illustrated in FIG.
2, a system area consists of three logical cells. Within the
logical cell area, all sub-areas transmit the same cell-id
information (e.g. scrambling code). In the case of a building,
cells A, B and C would cover different parts of the building
(floors).
[0031] If the network notices that the radio resource capacity must
be increased in some parts of the system area, it can split the
current logical cells into smaller logical cells, for example by
allocating a new set of downlink common channels on a new
scrambling code and/or frequency (indicating a new cell identity).
If the different sub-areas have a sufficient spatial separation,
the network can decide to reuse an old frequency or scrambling
code, instead of reserving a totally new one. FIG. 3 illustrates a
reconfiguration of the system area to provide five logical cells.
If the spatial separation between cells D and E is large enough,
the same radio resources can be used in both. Conversely, a number
of smaller logical cells can be merged into one larger cell, when
the capacity can be reduced.
[0032] During the logical cell splitting or merging transition
period, two sets of common channels must be transmitted within the
overlapping sub-area, i.e. channels associated with the old cell(s)
and channels associated with the new cell(s). This considerably
increases the amount of downlink interference assuming that the
same frequency is used both within the old and the new logical
cell(s). Furthermore, the amount of resources available for the
dedicated downlink channels is reduced. Therefore, the transition
should preferably be performed during "off-peak" hours when traffic
levels are low.
[0033] It will be appreciated that the solution presented here is
also applicable to a partial merging/splitting (or shifting) of
logical cells. In the case of such a partial merging/splitting,
only a part of a logical cell, i.e. a sub-set of sub-areas, is
merged into a neighbouring logical cell. In this way, the sizes of
neighbouring logical cells can be dynamically adjusted based on the
required radio resource capacity.
[0034] During a transition period, there are in principle two
different ways to start up the new logical cell, or to close down
the old logical cell: [0035] 1. Handover. The network orders the
mobile terminals to switch from the old scrambling code (and/or
frequency) to the new one. The downside of this solution is the
increased signalling in the network. On the other hand, the
transition period becomes quite short. [0036] 2. "Smooth
transition". Old connections are kept as they are, whilst all new
connections are set up towards the new logical cell. This approach
keeps the network signalling load under control and/or at a
minimum, although the downside is the possibly long transition
period (i.e. the time taken for all ongoing connections to
terminate).
[0037] Obviously, a combination of these two approaches is also
possible.
[0038] Once a transition has been finalised, the old logical
cell(s) can be switched off. However, if the new logical cell was
created on a different carrier frequency, both the old and the new
logical cells can co-exist if necessary. Thus, in such a scenario,
a new frequency layer has been set up ("floating multi-layer
structure"). This kind of deployment might be desirable if the high
capacity sub-area includes both slow and fast moving mobiles. From
a signalling point of view, it is more favourable to connect fast
moving mobile terminals into the larger logical cell, while more
stationary terminals located within the same service area could be
connected to a smaller logical cell. With this kind of network
deployment, the possible "near/far" and co-existence problems could
be considerably reduced, since both frequency layers are now
transmitted from the same physical node.
[0039] When looking at the network architecture, a central control
node, a kind of a partial combination of the current UMTS
Terrestrial Radio Access Network (UTRAN) Radio Network Controller
(RNC) and Base Station (BS) is needed. This control node decides
which small sub-areas are combined into the actual logical cell
areas. In order to be able to make this decision, the control node
needs some kind of information (measurement data) about the
required capacity from the different sub-areas. This measurement
data can consist of for example the average number of active links
or the measured total uplink interference per radio unit, or the
number of connection attempts.
[0040] A network operator may in some cases wish to connect users
of a certain service, e.g. packet switched data transmission, to
one logical cell whilst users of some other services, e.g. speech,
are connected to a different logical cell. With the present
invention, this kind of action ("service-based splitting of logical
cells") can be performed dynamically and in a simple fashion in the
desired location within the system area covered by the sub-areas.
However, as the users with different services are typically not
geographically separated, the new logical cell cannot operate on
the same frequency carrier as the original cell. Thus, the new
logical cell has to be created on another frequency leading to a
similar floating multi-layer structure as described above.
[0041] If a logical cell consists of multiple sub-areas, the
logical cell can be treated as a "distributed antenna system".
Since each sub-area is connected to a single centralized control
node, several different communication methods become possible.
[0042] Assume now that logical cell A consists of nine sub-areas
(A.sub.1 . . . A.sub.9), each of them individually connected to a
central control node B, as is illustrated in FIG. 4. Assume also
that a mobile C is located within the logical cell A. The same
common channel information is transmitted within all nine
sub-areas. However, it is not necessary to use all nine sub-areas
for exchanging information relating to user C. In fact, using all
sub-areas might in some cases result in a poorer performance than
using only a limited set of sub-areas. Therefore, it is suggested
that only the sub-areas that can really contribute to the overall
signal quality are used to carry traffic to/from user C. Assuming
that the uplink signal strength (RSCP) or the uplink quality (e.g.
Carrier-to-Interference Ratio, CIR) can be measured separately for
each sub-area and user, an appropriate sub-area selection can be
made. A relative sub-area selection is assumed to be applied, which
means that the sub-area which has the best measured uplink RSCP or
CIR is always included in the set of active sub-areas. In addition,
if other sub-areas can "hear" the same user with an RSCP or CIR
which is close enough to the best measured RSCP or CIR, they are
also included in the set of active sub-areas. The sub-area
selection is changed dynamically throughout the active connection,
and new sub-areas are added and old ones removed or replaced with
new ones, depending on the actual uplink measurement results with
minimum delay and at a minimum interference cost/impact.
[0043] In the downlink direction, the situation is similar to the
traditional (UTRAN) multipath/macrodiversity combining, where a
mobile terminal can track and resolve a number of signals with the
help of the RAKE receiver (basically the question is about maximum
ratio combining of the different paths coming from one or several
logical cells, depending on the soft handover situation). Assuming
that the different sub-areas are individually connected to the
central control node, several combining methods, e.g. selection
combining or maximum ratio combining, are applicable for the uplink
direction. However, in the case of a soft handover situation
between different control nodes, maximum ratio combining is most
probably not possible for the uplink direction. Thus, for such
situations, selection combining should be applied.
[0044] The maximum number of active sub-areas as well as the
criteria (i.e. thresholds) for the sub-area addition, removal and
replacement can vary from user to user, e.g. depending on the user
speed and estimated propagation conditions (channel profile).
Furthermore, the criteria can be different for the uplink and for
the downlink resulting in different numbers of active sub-areas for
each direction. The reason for this is that while macro diversity
is in principle always favourable for the uplink, in the case of
the downlink the overall macro diversity gain (similar to "soft
handover gain") is a trade-off between the macro diversity
combining gain and the loss due to the increased downlink
interference. Therefore, the selection of the active sub-areas is
not as sensitive for the uplink as it is for the downlink.
[0045] When the user is about to move from one logical cell to
another, a handover is required. If the new logical cell is
operating on the same frequency, a soft handover is possible. While
the user is in soft handover, and in particular if the new cell is
connected to the same control node as the old cell, the active
sub-areas should be selected from the combined group of sub-areas
(combined group consists of both the sub-areas belonging to the old
cell and the sub-areas belonging to the new cell), see FIG. 5. In
FIG. 5, the user (whose location is marked with a diamond) is
assumed to be in soft handover between logical cells A and C. Now,
the set of active sub-areas assigned for the user in question could
consist of {A.sub., A.sub.25, C.sub.3, C.sub.6} for the uplink, and
{A.sub.19, A.sub.25, C.sub.6} for the downlink.
[0046] Finally, since the central control node has full control
over all of the signals within the combined coverage area of the
logical cells which are connected to it, the control node can apply
special signal processing actions in order to improve the
performance of the network. Possible actions include for example
adding artificial delays between the different sub-areas within a
logical cell in order to create artificial multipaths, or
attenuating all or only some of the signals transmitted within a
certain sub-area, compared to the corresponding signals transmitted
from other (possibly neighbouring) sub-areas. If the whole set of
downlink signals or the set of downlink channels is attenuated, the
coverage area of the corresponding sub-area can be modified. If
only some individual dedicated downlink channels are attenuated (in
particular towards users in soft handover), the downlink macro
diversity gain could be slightly improved.
[0047] The above description assumes that the same dedicated
information targeted towards a certain user is transmitted from all
active sub-areas allocated to that user. Similarly, it has been
assumed that the same dedicated information from a certain user is
received at each of these active sub-areas. However, the invention
also provides for transmitting different dedicated information in
parallel from the active sub-areas, but still targeted towards the
specific user. Furthermore, in the uplink direction, the user
terminal can transmit multiple dedicated data streams in parallel,
and these data streams can then be received at the different
sub-areas. Traditionally, this kind of a transmission method has
been called as "multi-stream MIMO (Multiple Input Multiple Output)
transmission".
[0048] Due to the spatially separated transmit and receive
antennas, multipath fading between the different transmit-receive
antenna pairs becomes less correlated, reducing the interference
between the data streams, and making possible the re-use of
different kinds of radio resources, such as time, frequency and
codes. As a result, bit rates and network capacity can be
considerably increased compared to a single-stream
transmission.
[0049] Transmission power must be divided between multiple parallel
streams, and the multipath fading is not fully uncorrelated between
the antennas, and so it is recognised that multi-stream
transmission is favourable in scenarios where the obtainable SINR
(Signal to Interference and Noise Ratio) is sufficiently large. The
SINR is sufficiently large at locations that are not too far away
from the serving base station. It is also apparent that this kind
of intra-site antenna diversity does not provide any kind of
additional diversity against shadow fading, which has typically the
same value towards all co-located antennas. Therefore, the
traditional "multi-stream MIMO transmission" cannot be seen as an
efficient way to improve coverage.
[0050] The invention differs from the traditional method in the way
the transmit/receive antennas are organized on the network side.
Traditionally, the antennas are co-located at a site, but with a
sufficient spatial separation (a number of wavelengths) between
them. According to the invention, the antennas are not co-located,
but are distributed in different sub-areas. This considerably
increases the spatial separation between the antennas, and results
in uncorrelated multipath fading, as well as considerably reducing
correlated shadow fading. The use of "multi-stream transmission"
becomes different. When the antennas are distributed in different
sub-areas, multi-stream transmission is usable only when the
obtainable quality (SINR) at the different sub-areas is
sufficiently high, and also close enough from each other. Locations
that are close to the borders between the different active
sub-areas, but still close enough to the active radio transceivers
provide these qualities. The invention allows "multi-stream
transmission" to be used to improve the bit rates at the border
areas between the active sub-areas.
[0051] Considering a WCDMA system, the number of orthogonal
downlink codes (Orthogonal Variable Spreading Factor (OVSF) codes)
associated with one scrambling code is limited. It is therefore
possible to use several scrambling codes within one logical cell,
and in that way make the system always "interference-limited".
However, only one set of downlink common channels is transmitted
within each logical cell on the primary scrambling code. The
problem with multiple scrambling codes is that the links (OVSF
codes) using the same scrambling code are orthogonal with each
other, but links (OVSF codes) using different scrambling codes are
not. Therefore, a user on the secondary scrambling code typically
requires more downlink transmit power than a corresponding user on
the primary scrambling code, in particular if the network applies
an OVSF code allocation algorithm which aims to fully utilize the
primary scrambling code before adding a secondary scrambling code
into the logical cell. Now, with the help of the solution presented
here, better control over the usage of the multiple scrambling
codes can be accomplished.
[0052] Assume the example of FIG. 6 which illustrates a system area
consisting of three logical cells. Logical cell A contains a
traffic hot spot (hatched area; A.sub.29, A.sub.30, A.sub.35,
A.sub.36). Now, if the central control node notices that the
capacity required within the hotspot area increases and the
downlink capacity within logical cell A is starting to be
"code-limited", it can decide to split that area off into a new
logical cell D, as explained above. However, as an alternative, in
particular if the area in question is a relatively static traffic
"hot spot" with relatively stationary users (e.g. an office
building), the control node can as a first action add a secondary
scrambling code or codes into the logical cell A. Furthermore, the
users within the hot spot area should be allocated the primary
scrambling code, i.e. the scrambling code where the downlink common
channels are located, while users on the less loaded sub-areas
could be allocated the secondary scrambling codes. By doing so, the
cell/system capacity can be improved compared to the situation
where a random allocation of scrambling codes (from the user
location point of view) is applied.
[0053] When a user on a primary scrambling code moves out from a
"hot spot area", no "code handover" is required. However, when a
user on the secondary scrambling code enters the "hot spot area", a
code handover may be required in order to avoid (or to relieve) any
congestion. The obvious prerequisite is that there is enough room
available on the primary scrambling code.
[0054] With the help of the solution described here, a flexible
allocation of the downlink scrambling codes, downlink common
control channels, and carrier frequencies over the whole system
area becomes possible. For example, based on the actual traffic
load, large logical cells can be split into smaller ones, or
smaller logical cells can be merged into larger cells. In a similar
fashion, new inter-frequency cell layers can be created at the
wanted locations (i.e. the location area of carrier F2 can be
assumed to be "floating" with respect to the location area of
carrier F1). Finally, the allocation of multiple scrambling codes,
or to be more exact, the allocation of codes for specific users
within one logical cell, can also be based on the geographical
traffic distribution.
[0055] Key features of the solution are: [0056] The possibility to
have full and dynamic control of the logical cell areas within the
whole system area. [0057] The (transition) procedure when starting
up a new logical cell within an old logical cell area (cell
splitting), or when closing down a logical cell (cell merging).
[0058] Flexible generation of a floating multilayer structure
(macro-macro, macro-micro, macro-indoor, micro-indoor etc.),
assuming that the new logical cell is operating on a different
frequency from the old one. Both frequencies are transmitted via
the same radio units so that the lower layer with smaller coverage
area will use a sub-set of the radio units allocated for the higher
layer with a larger coverage area. [0059] The dynamic selection of
active sub-areas (for each user), which is based on the relative
uplink RSCP or CIR measurements. These measurements will be
performed by the network (at each radio unit or possibly at the
control node). [0060] The dynamic selection of active sub-areas
(for each user), which is based on the estimated user speed. [0061]
The dynamic selection of active sub-areas (for each user), which is
based on the estimated propagation conditions (channel profile).
[0062] Different active sub-area selection criteria for the uplink
and the downlink, and, as a result, partially different sets of
active sub-areas for the uplink and the downlink. [0063] When the
user is in soft handover between two or more logical cells
belonging to the same control node, the active sub-areas are
selected from the combined group of sub-areas. [0064] Allocation of
users on different scrambling codes within a logical cell depending
on the location of the user with respect to the locations of the
other users (location of the traffic in average).
[0065] It will be appreciated by the person of skill in the art
that various modifications may be made to the above described
embodiments without departing from the scope of the present
invention.
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